refers to a specific entry in a Japanese "Idol Image" or "Gravure" DVD series, which typically features models in themed photo and video shoots.
(桃瀬なつみ), a gravure idol active in the mid-2000s to early 2010s. Publisher: Athena Music Publishing dvd+cpsky+055+vol
荒木のぞみ引退スペシャル(CPSKY-159) [DVD] - Amazon.com refers to a specific entry in a Japanese
Collectibility and market value
Because many of these labels, including Shibuya Music, eventually ceased production or changed focus, original physical copies of CPSKY-055 are difficult to find. Today, they are primarily traded on Japanese second-hand specialty sites like Suruga-ya or Culture Station, where they can command high prices from collectors of Japanese media history. Cultural Context Today, they are primarily traded on Japanese second-hand
Put together, this looks like an intermediate or log filename created by DVD backup software while decrypting a specific disc title.
dvd+cpsky+055+vol is likely a technical artifact from a DVD decryption attempt. It’s not a standard video format and won’t play in media players. If you’re trying to back up a DVD, use modern, well-maintained tools instead of digging through cryptic file names.